The Internet makes it easy to offer large assortments of products, tempting managers to chase the “long tail”—that is, the phenomenon in which niche products gain a significant share of demand among all products. Yet few studies empirically examine the existence and drivers of this long tail phenomenon. This study uses a unique data set with 843,922 purchases from 143,939 customers that a monopolistic video-on-demand operator observed over 111 weeks after its launch of the service. The current analysis centers on the effects of increasing assortment sizes and improved search technologies on measures of the long tail, such as per customer demand, the share of products purchased from the assortment, the distribution of demand across products, and the concentration of demand. Increases in assortment sizes and better assortment quality lead to increases in demand per customer and a longer tail. The length of the tail (i.e., share of purchased products) is also driven by new customers and seasonal effects, such as school vacations, whereas the presence of high-quality blockbuster products shortens the tail. Different search technologies can shift demand toward niche products as well as toward blockbuster products.